You don't need to beat everyone. Just put your strongest party member in one party and plow through towards Kefka. I would go with Gau, Edgar, Celes, and Sabin.
Normal battles:
Gau - Rage Pterodon or Marshal
Edgar - Bio Blaster
Celes - Healing
Sabin - Fire Dance
Rider:
Gau should rage Rhodox, Dark Wind, or Commader for an instant kill. If you don't have those then Arenid or Primordite.
Kefka:
Gau - Arenid or Primordite
Edgar - Autocrossbow
Celes - Runic
Sabin - Aurabolt
The Coin-Op game list is close to complete. In about a year I will add another 100 Coin-Op games. Games of the Metal Slug quality will be right around the technical cut-off limit. Meaning Metal Slug might or might not make the cut.